APOLLO - NASA€¦ · • APOLLO is a millimeter-capable lunar ranging station with unprecedented performance • Given the order-of-magnitude gains in range precision, we expect

APOLLOAPOLLO

Status UpdateStatus Update

Dusty ReflectorsDusty Reflectors

LunokhodLunokhod 1 Found1 Found

Tom Murphy (UCSD)

photo credit: Jack Dembicky

2011.05.19 IWLR 17; Bad Kotzting 2

APOLLO: One small step for science…

…One giant leap for LLR

• APOLLO offers order-of-magnitude

improvements to LLR by:

– Using a 3.5 meter telescope

– Operating at 20 pulses/sec

– Using advanced detector technology

– Gathering multiple photons/shot

• Achieving millimeter range precision

– Tightly integrating experiment and analysis

– Having the best acronym

• funded by NASA & NSF

– Team includes T. Murphy, E. Adelberger, J.

Battat, C.D. Hoyle, N. Johnson, R. McMillan,

E. Michelsen, K. Nordtvedt, C. Stubbs, E.

Swanson

APO 3.5 m, New Mexico, 2800 m elevation

3.5 meter

2.5 meter Sloan Digital Sky Survey

laser

people

2011.05.19 3IWLR 17; Bad Kotzting


Breaking All Records

� APOLLO has greatly surpassed previous records

� roughly 70 times OCA rate on Apollo reflectors

� APOLLO can operate at full moon

� Often a majority of APOLLO returns are multiple-photon events

� record is 12 photons in one shot (out of 12 functioning APD elements)

� APD array (many buckets) is crucial

� APOLLO has greatly surpassed previous records

� roughly 70 times OCA rate on Apollo reflectors

� APOLLO can operate at full moon

� Often a majority of APOLLO returns are multiple-photon events

� record is 12 photons in one shot (out of 12 functioning APD elements)

� APD array (many buckets) is crucial

Reflector

APOLLO max

photons/5-min

APOLLO max

photons/shot

(5 min avg)

Apollo 11 5395 (65×) 0.90

Apollo 14 9125 (69×) 1.52

Apollo 15 18875 (67×) 3.15

Lunokhod 2 900 (31×) 0.15

(relative to pre-APOLLO record)


APOLLO Data Campaign

• Steady accumulation of data; less reliance on Apollo 15 over time

• Found Lunokhod 1 in 2010


APOLLO Data Quality

• Uncertainties are per night, per reflector; pre-APOLLO sub-centimeter rare

• Medians are 2.4, 2.7, 2.4, 1.8, 3.3 mm for A11, L1, A14, A15, L2, resp.

• Combined nightly median range error is 1.4 mm


Next Step: Model Development

• Extracting science from LLR data requires a model that includes all the

physics that can influence the Earth-Moon range

– N-body relativistic gravity in solar system

– body figure torques

– site displacement phenomena

• The best LLR models currently produce > 15 mm residuals

• Many few-millimeter effects are not yet included

– crustal loading phenomena from atmosphere, ocean, hydrology

– geocenter motion (center of mass with respect to geometry)

– tidal model needs improvement

– atmospheric propagation delay model needs updating

– Earth orientation models could better incorporate LLR data

– multipole representations of Earth and Moon mass distributions need

improvement

Example: Adjusting Lunar Orientation


APOLLO data clearly call for orientation adjustments each night (vertical bands)

• Apollo 11

• Apollo 14

• Apollo 15

• Lunokhod 2

Re-orienting all the models


10 nrad

is 17 mm

at the Moon’s

surface

A closer look at the best model (JPL)


More weight to APOLLO data � model does better on orientation

90 180 270 3600

100

50

0

10

Reflecto

r S

tren

gth

(%

)

Lunar Phase

Reflector Degradation

what we expect

what we really get…

10%1% the full moon curse



APOLLO rates on Apollo 15 reflector

full

moon

background level

in a 1 ns bin


More on the deficit

• APOLLO system sensitivity is not to blame for full-moon deficit

– background is not impacted

• Early LLR data trucked right through full-moon with no problem

• The deficit began to appear around 1979

• No full-moon ranges from 1985 until 2006, except during eclipse

1973 - 1976 1979 - 1984

What’s Wrong?

• The full-moon deficit, together with normal eclipse behavior, gives us the best clues:– thermal nature

– absorbing solar flux

• Most likely: dust– Obviously could explain overall deficit

(10%)

• Full moon effect then due to solar heating of dust– sun comes straight down tube at

full moon

– makes front hotter than vertex of corner cube, leading to divergence of exit beam

– only takes 4°C (7°F) gradient to introduce 10× reduction

cool, quick route

warm, slow road


Eclipse Opportunity

• On December 21, 2010 (UTC), a perfectly-positioned eclipse

gave us a celestial light switch

– verified that sunlight is responsible for full moon curse

– examine response time: is it thermal effect in corner cubes?

perfect eclipse for North Americaperfect eclipse for North America


Eclipse Pics

2011.05.19 IWLR 17; Bad Kotzting 16photo credits: Jack Dembicky

Illu

min

ation;

Therm

al G

radie

nt;

Retu

rn S

treng

th

Time

Cartoon of Expectations


hot face

cold face

zero crossing

response peak

Preliminary Eclipse Results

full shadow

robust recovery initially, then down, and brief resurgence once light returns


� Apollo 11

� Apollo 14

� (Apollo 15)/3.0

historical peak range @ F.M.


The Lunokhod 1 Reflector

•• 1414 triangular CCRs, 11 cm side length

• Landed November 1970

• Sporadic early reports of Soviet and French ranging; no records

persist

• Identical design to later Lunokhod 2 reflector– would expect L1 to be weak, like L2…or worse


Enter LRO

•• TheThe LunarLunar Reconnaissance Orbiter (LRO) paved the way:

– LROC imaging (March 2010) found the rover and provided coordinates

– LOLA altimetry fixed the site radius

– LRO corner cube array prompted APOLLO to develop wide gate

1734.927 km


APOLLO Find, 22 April, 2010

• Armed with 100 meter accurate coordinates, APOLLO’s first favorable telescope time produced stunning results

• Offset was 40 m (270 ns) in projected range (100 m lateral), putting signal at edge of gate

• Gate adjustments in first run confirmed reality

• Almost 2000 photons in first try: so bright we thought we were being fooled

signal

gate adjustments

background

Your discovery gives hope to all of usYour discovery gives hope to all of us

who lost something during the seventieswho lost something during the seventies……

−− Ed LeonEd Leon

Apache Point ObservatoryApache Point Observatory



Current Error Ellipse• Based on a few months of

observation at a limited sampling of

librations, we have a centimeter-

level position determination

• Error ellipses are 1σ, 2σ, 3σ

• Best-fit position, in DE421 Principal-

Axis coordinates:

– r = 1734928.72

– lat = 38.3330784°

– lon = -35.036674°

• Location of L1 makes it especially

valuable for science


Potential Impact on Science

• L1 is the farthest reflector from the

apparent lunar center

• Offers best leverage on libration

determination

– key for C.o.M. motion → gravity

– also for lunar interior study

• Unlike Apollo reflectors, L1 (and L2)

offer both latitude and longitude

libration sensitivity

• More reflectors probe tidal

deformation

Reflector θ from center

libration sensitiv.

longitude sensitiv.

latitude sensitiv.

A11 23.5° 0.40 0.40 0.01

A14 17.9° 0.31 0.30 0.06

A15 26.4° 0.44 0.06 0.44

L1 50.0° 0.77 0.45 0.51

L2 39.5° 0.63 0.46 0.37


Summary & Next Steps

• APOLLO is a millimeter-capable lunar ranging station with unprecedented performance

• Given the order-of-magnitude gains in range precision, we expect order-of-magnitude gains in a variety of tests of fundamental gravity

• Our steady-state campaign is now 4.5 years old

– began October 2006, one year after first light

• Now grappling with analysis in the face of vastly better data

– much new stuff to learn, with concomitant refinements to data reduction and to the analytical model

– plans to develop open source LLR/planetary analysis code

• Some surprises along the way

– degradation of reflectors

– found lost Lunokhod 1 reflector; now have 5

Documents

APOLLO - NASA€¦ · • APOLLO is a millimeter-capable lunar ranging station with unprecedented performance • Given the order-of-magnitude gains in range precision, we expect